Sinhalite

Chemical formula: MgAlBO<sub>₄</sub>

A rare magnesium aluminum borate, valued as a gemstone with colors ranging from yellow and green to brown.

## Characteristics Sinhalite is a rare mineral from the borate group, which for many years was mistakenly identified as brown peridot (olivine). Its name comes from "Sinhala," the Sanskrit word for Sri Lanka, where it was first correctly identified. It occurs as well-formed, prismatic or tabular crystals, but is most commonly found as rounded grains and pebbles in alluvial deposits. Clear, transparent specimens with vibrant color are highly prized and used in jewelry. ## Physical Properties Sinhalite is characterized by significant hardness, ranging from 6.5-7 on the Mohs scale, making it a durable gemstone. It has a vitreous luster and is usually transparent to translucent. The mineral's density ranges from 3.47 to 3.50 g/cm³, which is a relatively high value and helpful in diagnosis. ## Colors and Varieties The color palette of sinhalite extends from pale yellow, through honey shades, greenish-yellow, olive-green, to intense brown and reddish-brown. The most sought-after stones are those with vibrant, saturated colors without gray or dull tones. There are no distinct commercial varieties, and classification is based primarily on color and its intensity. ## History and Name The mineral was formally described and named in 1952 by G.F. Claringbull and M.H. Hey of the British Museum. They discovered that many stones from Sri Lanka, long classified as peridots, were in fact a new, previously unknown mineral species. The name directly refers to the historical name of the island, which is the main source of this mineral. ## Uses Due to its rarity, attractive appearance, and good physical properties, sinhalite is primarily a gemstone and collector's item. Faceted stones adorn rings, pendants, and earrings. Specimens with poorer transparency or inclusions are destined for specialized mineralogical collections.

Properties

Mohs hardness: 6.5-7
Luster: Vitreous
Streak: White
Density: 3.47-3.50
Cleavage: Indistinct
Fracture: Conchoidal to uneven
Transparency: Transparent to translucent
Crystal system: Orthorhombic

Diagnostic features

## Identification Key diagnostic features of sinhalite include its characteristic colors (shades of yellow, green, and brown), high density (easily noticeable "weight" in hand), and strong pleochroism, i.e., a change in color shades depending on the viewing direction (usually from pale yellow through greenish-brown to dark brown). It also has a high refractive index, which translates into good brilliance in faceted stones. ## Distinguishing from Similar Minerals Sinhalite is often confused with many other gemstones. It is distinguished from peridot (olivine) by its higher density and different optical properties (peridot has stronger double refraction, often visible to the naked eye as a doubling of facet edges). It is distinguished from zircon by its lower dispersion (lack of "fire" characteristic of zircon) and lower density. Chrysoberyl is harder (8.5 on the Mohs scale). Identification often requires the use of specialized gemological tools, such as a refractometer and hydrostatic balance. ## Crystal Forms It crystallizes in the orthorhombic system. Crystals usually have a prismatic habit, often elongated. It also occurs as irregular grains or rounded pebbles in alluvial deposits, which is a result of fluvial transport.

Geological environment

## Genesis Sinhalite is a mineral of metamorphic origin. It forms in contact zones, in rocks rich in magnesium and aluminum, which have been subjected to boron-rich fluids. A typical environment for its occurrence is skarns formed at the contact of granitic intrusions with dolomites or magnesian limestones, as well as in some gneisses and granulites. ## Mineral Associations Minerals that often accompany sinhalite include spinel (especially pleonaste), phlogopite, chondrodite, diopside, sapphire, and minerals from the tourmaline group. The occurrence of these minerals together with sinhalite is an indication of the conditions of its formation. ## Localities The most important and historical source of gem-quality sinhalite is Sri Lanka, especially the alluvial deposits in the Ratnapura region. Significant quantities, including well-formed crystals, come from Myanmar (Burma), especially from the Mogok area. Other known localities include Madagascar, Tanzania, and China. Occurrences have also been reported in the United States (New York, New Jersey), but these are not of gemological significance.

Rarity

Rare

For collectors

## Quality Criteria The most highly prized sinhalite specimens are characterized by an intense but not too dark color – especially sought after are vibrant golden-brown, honey, and greenish hues. High transparency and the absence of eye-visible inclusions are crucial. Large, clean stones over 5 carats are very rare and command high prices. In the case of crystalline specimens, the value is enhanced by a well-formed, undamaged crystal habit and its size. ## Market Prices The prices of faceted sinhalites vary widely. Small stones (below 1 carat) of average color can cost from several tens to about 100-150 USD per carat. Stones of better color and clarity in the 1-3 carat range fetch prices of 200-500 USD per carat. Exceptional specimens over 5 carats, with saturated color and excellent clarity, can be valued at 1000 USD per carat or more. ## Popular Localities Collectors most desire specimens from classic localities. Stones from Sri Lanka, often with beautiful brown and yellow hues, have historical value. In turn, specimens from Mogok in Myanmar are known for occurring as well-formed crystals, often in association with other rare minerals, which makes them extremely attractive to mineral collectors, not just gemstone collectors.

Care and storage

## Cleaning Sinhalite is relatively hard and durable, which makes it easy to care for. The safest cleaning method is to use lukewarm soapy water and a soft brush (e.g., a toothbrush). After washing, rinse it thoroughly and dry it with a soft cloth. It is resistant to ultrasonic cleaners, but caution should be exercised if the stone has internal fractures or numerous inclusions. ## What to Avoid Avoid contact with strong acids and bases, which can damage the stone's surface. Despite its good hardness, it is not resistant to sudden temperature changes, which can lead to internal fractures. Also, protect it from strong impacts and contact with harder materials (e.g., diamond, corundum), which can scratch it. ## Storage It is recommended to store sinhalite jewelry and collector's specimens separately, in a soft pouch or in a padded box with compartments. This prevents accidental scratching by harder stones and scratching of softer minerals and metals by sinhalite.

External references

https://en.wikipedia.org/wiki/https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FSinhalite